HBC Nantes otherwise had a bright start to the match when they levelled the two-goal deficit from the reverse fixture, leading 2-0 thanks to Thibaud Briet, and until the 14th minute, the visitors preserved their two-goal gap.
Barça then struck back, and by scoring three successive goals, they went into the break with a three-goal lead, paving the way for the win.
Both goalkeepers, Emil Nielsen (Barça) and Ignacio Biosca (Nantes), showed brilliant form throughout the encounter, and despite the hosts’ half-time lead, HBC’s Spaniard led the statistics with 11 saves compared to Nielsen's eight.
After the break, it took the Champions League record winners only 10 minutes to virtually secure their ticket to Cologne, leading 21-15 and extending the overall margin to eight goals, which was extended to 12 goals.
It was the 14th time that Barcelona qualified for the Champions League Final Four, more than any other club. They won the trophy most recently in 2004.